Tuesday, October 02, 2007


Premolar Extractions Controversy

There is probably no facet of orthodontic treatment that has caused as much controversy as the decision to extract, or not to extract, permanent teeth: and more specifically, whether to extract four premolars or to “develop” room for non-extraction treatment.

Besides the obvious reasons of avoiding the trauma and expense of surgery, and the desire to preserve permanent teeth; other alleged negative sequela, such as TMD problems, flattened facial profiles, and “dark buccal corridors” have contributed to the premolar extraction controversy. Like a pendulum, the popularity of premolar extractions has swung back and forth, between the extremes of non-extraction at any cost and “routine” extractions to achieve arbitrary cephalometric norms.

Some of the factors we consider are:

When dealing with a fairly “normal” orthodontic problem (no gross asymmetries) the decision to extract four premolars is straightforward although often not easy. It is impossible to extract less than a whole tooth, and usually the extraction of a tooth on the left requires an extraction on the right to balance the midline. Likewise, lower extractions usually require upper extractions (and visa versa) to prevent excessive overjet or underbite. These parameters normally lead to extraction of four first premolars or to treat as a non-extraction case. There are times when upper premolars only, a single lower incisor extraction, molar extraction, or interproximal enamel reduction (IPR) are appropriate but, in general, the decision for extractions is often framed around “4-bi’s”.

Given the usual all or nothing nature of the premolar extraction decision, it is no surprise that different orthodontists often appear to have conflicting treatment plans for the same patient. The reason is not that they see very different problems or have radically different philosophies of treatment, but rather that each doctor has a different line in the gray area between extractions and nonextraction. Two treatment plans that appear very different can both be based on a similar analysis of the patient’s problem, but end up with very different treatments due to the black and white nature of the decision making process.

It is important to understand that in borderline cases there are no correct or right answers. Both treatments performed by competent orthodontists would produce a good result, but neither is perfect. Each option would have pros and cons, and orthodontists and dentists could (and do!) spend endless amounts of time debating which option is “right”.

We try to avoid extractions as much as possible, but extractions should be considered when esthetics and stability call for it. Truthfully, almost any patient can be treated without extractions and, often, this is technically the easier way. This is the reason that the weekend orthodontic courses aimed at general dentists almost always stress nonextraction treatment.

Where there is a conflict between facial esthetics and dental stability, it is our judgment to favor esthetics. This is not to say that patients with flat facial profiles and extreme crowding should be treated without extractions, nor that patients with full profiles and large tongues should have teeth extracted, but rather that esthetics should be the primary determinant of treatment in any borderline situation. In these cases it is very important that the patient understands the necessity of long-term retention

Contrary to the beliefs of many nonextraction proponents, good scientific studies (evidenced based) done on TMD and orthodontic treatment fail to show any correlation between the development of TMD type problems and the extraction (or nonextraction) of teeth. All dentists can remember patients who develop TMD problems after extraction treatment and, if you feel there is a correlation, you will fixate on these patients. Statistically, you are just as likely to find TMD problems in patients treated nonextraction or, for that matter, patients who never received orthodontic treatment at all.

Scientific studies have also shown that well treated extraction cases do not adversely affect facial profiles. Again, it is easy to visualize patients with flat profiles who have had premolar extractions. Assuming a good treatment decision, these patients would have had a flat profile even if they never had treatment (and an extremely unstable dental alignment if they had been treated without extractions). The truth is: tight facial structures (flat faces) lead to crowding, which leads to extraction rather than extractions cause flat faces. As a matter of fact, the most dished in and flattened faces often belong to those patients whom we have treated without any extractions. Like the TMD controversy, negative esthetic effects attributed to extractions fall into our favorite logical fallacy “post hoc ergo propter hoc” (after this therefore because of this). Other studies have also shown that dark buccal corridors and a narrow smile are not “caused” by premolar extractions.

A good selling point for premolar extractions can be a patient with moderate crowding and well-formed and positioned third molars. Treated without premolar extractions this patient usually needs third molars removed. Extract premolars, close some of the space by mesial movement of the posterior teeth, and hopefully the thirds can erupt and be kept—an exchange of four small, easily removed teeth for four molars that would be difficult to extract. Unfortunately no guarantee can be made that the thirds will always come in with enough room.

There seems to be a great deal of confusion about early expansion treatment (AKA arch development or growth modification). There is a important difference between expanding a constricted upper arch to match a normal lower arch (OK) and significantly expanding both arches in a patient whose arches may be narrow, but are in a normal transverse occlusal relationship to each other (not OK). Although it is possible to upright lingually verted lower posterior arches (which may have collapsed in, to compensate for a narrow maxillary arch), it is not possible to expand the mandibular basal bone, as there is no suture to distract as in the maxilla. Of all the inviolate “facts” of orthodontics, one of the most established is the stability of the lower inter-canine width. Expansion beyond the original width is almost a guarantee of collapse and recrowding.

Every decade or so a new “magic bullet” comes along promising the ability to create space and avoid extractions or unstable expansion. The latest iteration of this is the Damon™ orthodontic bracket with its manufacturer’s promise of extremely light forces that “grow” more room than regular braces. As usual, no good science backs up these claims!

In an attempt to avoid first premolar extractions, various alternatives can be considered:

o Expanding the arch, especially in a flat-faced individual, is often preferable to extractions, with the understanding this is an unstable correction and perpetual detention will be needed.

o For patients with a good posterior occlusion, a good upper arch with relatively small upper incisors, moderately severe lower crowding, and minimal overbite, the extraction of a lower incisor can be considered. Extraction of an incisor should be evaluated very carefully, for it can result in an untreatable problem with excessive overjet/overbite in the wrong individual.

o Interproximal enamel reduction (IPR) can provide a moderate amount of room but should be reserved for older patients. Excessive IPR as an initial treatment complicates the orthodontist’s ability to correct minor relapses in the future.

o Consider extraction of second premolars rather than first premolars. Theoretically, this reduces the amount of anterior retraction when only some space is needed for crowding and the facial profile is acceptable. This works best when the second premolars resemble the first, but large, molar-like second premolars may provide too much room and small, canine-like first premolars may not work against first molars.

o Distilization of full arches is very difficult so extraction of third molars or even second molars to provide anterior room has never been shown to provide significant space. With the advent of temporary anchorage devises (TAD’s) this may become a “new” way to treat nonextraction…. we’re already trying it!

Bottom line: Extractions are just a tool, not good or bad in themselves. Used right, they improve the quality of treatment, used wrong they may create a poor result.

Class II

Our second topic: why are there so many ways to correct “Overbites”

Class II malocclusions or overjets (commonly, but incorrectly, called “overbites”) are one of the most common problems in orthodontics. Despite the customary Angle Class II classification, patients who exhibit excessive overjets are not a homogeneous group. The following all can produce excessive overjets.

Ø Protrusive maxilla
Ø Deficient (retrognathic) mandible
Ø Good posterior occlusion (Class I) with flared upper incisors
Ø Good posterior occlusion (Class I) with lingually verted lower anteriors
Ø Good skeletal alignment but the maxillary dentition is mesial to the mandibular dentition
Ø And of course a combination of 2 or more of the above problems

In addition to these sagittal problems, the vertical facial pattern influences the degree of overjet and the ease of correction. Further complicating the correction is the amount of growth the patient has left, as all class II problems are much harder to deal with when the patients are skeletally mature.

Understanding that Class II’s encompass a variety of problems makes it easier to see why there are a variety of ways to correct these problems. And, going with the theme of our newsletters, different orthodontists have different “philosophies” on how to achieve this correction.

As every orthodontist will tell you: most class II malocclusions are caused in large part by a deficient mandible. So why has so much traditional orthodontic treatment been aimed at retracting the maxilla and maxillary teeth with the use of headgears, molar distilizing appliances, upper premolar extractions and elastic band wear? The simple answer is: “its hard to grow mandibles” (some would even say it is impossible to “grow” mandibles!) Unfortunately computers don’t know this, and many patients are “promised” great facial improvements with the newest patient education software; and orthodontic companies and labs have an incentive to sell these innovative appliances. The fact that a promoter can show you anecdotally a patient who seems to have had a great response to a “mandible grower appliance” is no guarantee that this can be done on a regular basis.

Over the years various appliances such as the removable functionals e.g., Bionators, Activators, Frankels, Twin Blocks, Monoblocks, and the fixed “functional” appliances e.g., Herbst, MARA, Forsus, have been tried with the aim of stimulating mandibular growth over and above what would normally occur. As they have been “introduced” they were met with a great deal of enthusiasm followed unfortunately, a few years later, by disillusionment and a jump to the next silver bullet. Nonetheless many orthodontists (and general dentists) believe very strongly in this type of treatment. Why is that? Well often they do seem to work! Overjets do correct, but the big question is: do they “grow” mandibles and if they don’t are they worth the effort?
Being human we often see what we want to see. If we put in an appliance promoted to “grow” a small lower jaw and 6 months later the overjet is corrected, the logical assumption is that the appliance did what we wanted it to do! The facts however are that growing mandibles is one aspect of orthodontic treatment that has been well studied. The scientific consensus is that there is no or minimal long-term increase in mandibular growth over what would have been expected from normal growth. The overjet correction was really obtained in the same fashion as traditional orthodontic treatment: incremental improvements of the maxilla, mandible, and both dentoalveolar arches. Of course there are cases where one can show very significant improvements in mandibular position with the use of these appliances, but these cases are unusual and unpredictable, and probably would have occurred with more traditional treatment. Nevertheless we do use these appliances; sometimes because they require less patient cooperation (the fixed versions), and sometimes because the patient is so obviously mandibular deficient that we hope that we may get lucky and get a great response.

So what are some of the more predictable treatment options for “overjets”?

Ø In growing individuals headgears still work well to slow the maxilla’s normal forward growth and let the mandible catch up. Sometimes this is a good option while waiting for tooth eruption and fixed appliance therapy and a great option if the maxilla is protrusive. Of course getting sufficient wear is a major problem.
Ø For patients with mild to moderate class II’s, elastic bands work well but they have the “side effect” of pulling the lower dentition forward off the bone support. There is an esthetic and stability limit to how protrusive the lower anteriors can be. And, with the natural mesial movement of the teeth in the arches over time, excessively protrusive anteriors can become unacceptable 10, 20 and 30 years later. For patients with crowding, the excessive lower protrusion can be overcome with lower extractions. Although much easier than headgears, elastic cooperation can be a problem with certain patients.
Ø Upper first premolar extractions can be used; especially with severe Class II’s with good lower arches in nongrowing patients. Care must be used not to overly retract the incisors relative to the facial profile. A major advantage is the ability to avoid patient cooperation problems and negative forward movement of the lower arch. Contrary to some “experts” no negative TMJ problems are associated with this treatment.
Ø Noncooperative molar distilizing appliances e.g., Pendulum, Wilson. Reciprocal mesial movement of the anterior teeth however usually limits the effectiveness of these appliances. Although promoted as not needing patient cooperation, Class II elastics are often required to back up these appliances.
Ø Often the best treatment is a camouflaged, compensated dentition with the upper anteriors slightly lingual and the mandibular anteriors slightly flared.
Ø For some severe problems ideal overjet cannot be obtained without using techniques that the patient rejects (surgery, extractions, braces, etc.) For these patients a Hollywood Smile (straight teeth but an uncorrected “bite”) can be offered
Ø Notwithstanding the Align Technologies computer animation showing overjet correction, it is extremely difficult to correct significant Class II malalignment with Invisalign.
Ø Perhaps one of the most exciting new advances in orthodontics may be the use of implants or temporary anchorage devices (TAD’s) that provide anchorage without the negative reciprocal mesial movements.

Bottom Line: how do we treat these patients? We weigh all the factors including the severity of the problem, likely patient cooperation, predictability of correction, facial esthetics (and on and on ….). In the end there are many ways of achieving a good correction and it is our job to come up with the best way for each individual patient. Not only should different techniques be used for the different types of Class II’s but, since there are positive and negative effects for each technique, different approaches are possible for the same problem.
To say that upper premolars should never be removed or that headgears are no longer needed is to take valuable tools out of the orthodontist’s armamentarium. And when the only alternative for full correction is full braces and a surgical procedure what’s wrong with giving a patient (after going over all of the alternatives) straight teeth and less than “ideal” bite? Sure there are negatives to various approaches but sometimes the alternatives are no better or even worse. It is the orthodontist’s responsibility to evaluate the pros and cons of the various techniques and, in consultation with the patient, parents and dentist come up with the best option for each patient... and this is what we try to do!

Third Molars

Our first topic: “post hoc ergo propter hoc” or why third molars don’t cause orthodontic relapse.

The orthodontic literature is pretty clear that, in general, third molars do not cause orthodontic relapse or crowding. The reason why this is such a strongly held belief is that it is almost “normal” for the anterior teeth (especially the lower incisors) to crowd up in the late teens or early twenties. This happens whether or not the patient had braces (or even wisdom teeth) and is probably related to late mandibular growth and a flattening of the anterior facial profile. Since this is the same time that the wisdom teeth “try” to erupt it is very easy to confuse cause and coincidence. The Latin phrase that speaks to this logical fallacy is: “post hoc ergo propter hoc” which translates “after this therefore because of this”.
This is not to say that there are not good reasons to extract the third molars, but that these reasons have more to do with whether the third molars can erupt into a self cleaning area or whether they will stay impacted and resorb roots or cause cysts. These are questions best left to the long-term evaluation of the patient’s general dentist.
The dental arches do not expand much as a child ages but they do get longer with the first molars erupting distal to the primary teeth, the second molars farther distal and finally the third molars. Unfortunately most of the time growth is complete before sufficient room is created for the third molars.
It is often the case that even with additional room provided by premolar extractions and some mesial movement of the molars during space closure there is still insufficient room for the thirds. For this reason we cannot even “promise” a patient that extracting premolars is really a trade where we extract four easily removed teeth (premolars) to save four bigger and more difficult to remove teeth (third molars).
In some borderline cases surgical removal of the distal gingival tissue can allow the patient to keep the third molars clean.
Bottom line is that the dentist must make a decision when growth is complete if there sufficient room for the third molars to come in to a self-cleaning area. If there is room, but the third molars are not coming in correctly, then a decision has to be made whether it is worth it to place partial orthodontic appliances to get the third molar aligned or just extract them as “unnecessary” teeth. Of course it is always hard to get a 20 year old to consent to further orthodontic treatment but sometimes they would rather do some ortho than some oral surgery!
As the above items point out there is nothing extra that the orthodontist can add to the decision as to whether to extract the third molars except in those rare cases when there is sufficient room but the third molars are erupting incorrectly and the patient would consent to additional orthodontic treatment.

Hope this helps!


Robert M. Waxler, D.M.D., M.S.
Jeffrey T. Cavanaugh, D.D.S.
For Century Orthodontics


Topics for our next letters may include:
Class III growth
Class II correction techniques (pros and cons)
Clear Appliance Therapy (CAT) appliances (Invisalign and OrthoClear)
Wires and brackets

If you have any request please let us know (century@centuryorthodontics.com)